1. Field of the Invention
The present invention relates generally to agricultural seeders that produce open furrows in the soil into which seeds are placed, and more particularly to an improved furrow closing system that provides a gentle and consistent closing of furrows in no-till seeding conditions.
2. Description of the Prior Art
Agricultural planting methods continue to improve in response to rapid worldwide adoption of no-till crop production techniques, in which the new crop's seeds are placed directly into the previous crop's stover, also known as stubble or crop residues. No-till seeding differs greatly from seeding into a tilled seedbed. The soil conditions for no-till seeding are typically wetter than those dried by tillage, due to the mulching effect of the crop residue remaining on the soil surface. Wetter soils are more prone to compaction by implements traveling over or engaging the soil. No-till soils are also typically more structurally stable than tilled soils, as the soil particles are "aggregated" or held together by old roots, fungi, and other organic material binding the particles together. Agricultural seeders operating in no-till conditions are often equipped and adjusted to employ more down pressure, either via coil spring or hydraulics, on the furrow opening disc to aid in the slicing of old crop residues and to assist in the penetration of this more structured soil. The extra down pressure on the opener disc and depth-gauging wheel sometimes results in more compaction of the furrow sidewall.
Especially in no-till, some difficulties are encountered when attempting to draw soil back into the furrow, which is desirable to protect the newly placed seeds from drying winds and sun, to protect from predation, and to improve seedling uniformity of growth. In tilled soils, the prior art was to employ packing wheels rearward of the furrow openers. The packing wheels operated to both close the furrow and to do some amount of packing, since in the loose and dry tilled soils packing is desirable to assist the seed in drawing moisture from below the seed. In no-till seeding, the wetter and more structured soils prevent packing wheels from performing adequately. The sidewall of the furrow formed in no-till seeding does not crumble easily like the sidewall in the tilled conditions, where the soil had previously been loosened and fluffed by tillage. Accordingly, very high pressures are sometimes employed on the packing or closing wheels in an attempt to squeeze the furrow sidewalls back together. This typically results in poor seedling emergence because the seedling has great difficulty pushing itself through this dense layer of soil.
Some improvements have been made by separating the seed firming and fir row closing functions. This is typically only possible where the depth-gauging function is already accomplished independently of the packing or closing wheel, as in the configuration where depth-gauging wheels travel alongside the furrow opening discs. Seeds are firmed into the soil in the bottom of the furrow by a narrow rolling wheel or sliding-type firmer exerting a slight amount of pressure onto the seed after it has been placed by the furrow openers and seed-directing tube. Since the closing wheel is now relieved of its packing function, the closing wheel may comprise a cast iron wheel with a sharp beveled edge or a spoked or tined wheel. Several spoked closing wheel types have been invented, as shown, for example, in U.S. Pat. No. 5,443,023 issued to Carroll, U.S. Pat. No. 5,497,717 issued to Martin, and U.S. Pat. No. 5,896,932 issued to Bruns et al. These spoked closing wheels all operate at angles and alignments inherited from conventional equipment designed to function in tilled seedbeds, and are not particularly suitable for either the spoked design or no-till seeding conditions. The results vary depending on the exact spoked wheel employed and the soil conditions, but generally the closing is characterized by a squeezing or packing action, the furrow is not adequately covered, the sidewall is not adequately shattered, and/or the seed placement is disrupted either by the spokes themselves or by the lifting of the sidewall during the shattering event and the spoke exit.
In the current state of agricultural seeder manufacturing and usage, some dichotomy has arisen between "planters" and "grain drills" (or simply "drills"). The dichotomy is not particularly relevant to this application, except in the ease of describing the prior art. For clarity, the term "planter" commonly refers to a seeder with the capability of singulating seeds for each opener unit's placement, and typically has a relatively wide spacing between individual opener units ("opener unit" refers to the entire seed placement apparatus for one furrow, including not only the furrow opening device, but also seed-directing tube, gauge wheel, firming and closing devices, linkages, and so forth). Planters almost universally utilize two furrow-opening discs on each opener unit, mounted immediately adjacent to each other and in contact with each other at their lower leading edge, but slightly away from each other toward their upper and rearward edges, which allows for a seed-directing tube between them. Planters employ depth-gauging wheels on the outside of each disc. Planters typically have a vertically pivoting bracket mounted rearward of the opening discs. The bracket holds the closing wheels inclined at approximately 20.degree. from the vertical and 0.degree. from the direction of travel.
The term "grain drill" commonly refers to a seeder lacking the capability of seed singulation; instead the seed is metered volumetrically. Drills tend to have the opener units mounted to achieve narrow row spacing, although the openers may be mounted in a staggered pattern on two or more ranks. Drills are manufactured employing a wide variety of furrow openers, including non-rolling openers referred to as "hoe," "knife" or "sweep" depending on the shape of the sliding component used, and both single- and double-disc openers. Of particular relevance to this application are disc-opener drills employing depth-gauging independent of the closing or firming mechanisms. Such drills are readily adapted to use the furrow closing system described by this application.
One popular drill employing separate depth gauging and furrow closing is manufactured by Deere and Company, of Moline, Ill., and sold as the Model No. 750 and its derivatives, the 752, 1850, 1860, and 1560. The 750-style opener unit has closing wheels inclined at 20.degree. to 24.degree. from the vertical and approximately 8.degree. from the direction of travel. Lateral alignment of such closing wheels is adjustable within a narrow range, usually maintaining the wheel approximately 3/4 inch from the lip of the furrow or about 1 1/8 inch from the midpoint of the furrow. Another popular drill employing separate depth gauging and finning/closing functions is the Flexicoil Model F/SO opener marketed on a variety of toolbars. The F/SO combines the firming and closing functions in one solid rubber wheel adjustable in a small range of vertical and horizontal angles, approximately from 0.degree. to 10.degree. from the vertical and 0.degree. to 10.degree. from the direction of travel.